use Parameter.empty instead of _empty

Author: ndgrigorian

examples/python/_runner.py

@@ -20,7 +20,7 @@
 
 def has_nondefault_params(sgn):
     for v in sgn.parameters.values():
-        if v.default is inspect._empty:
+        if v.default is inspect.Parameter.empty:
             return True
     return False